Transistor amplifier for capacitor-coupled vertical deflection coils in television



y 9, 1968 HANS-DIETER SCHNEIDER 3,3

TRANSISTOR AMPLIFIER FOR CAPACITOR-COUPLED VERTICAL DEFLECTION CCILS INTELEVISION Filed Nov. 14 1966 2 Sheets-Sheet 1 Fig.1

Fig.2

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.7nvenfor: Hans-Dieter Schneider J y 9, 1968 HANS-DIETER SCHNEIDER 9 307 TRANSISTOR AMPLIFIER FOR CAPACITOR-COUPLED VERTICAL DEFLECTION COILSIN TELEVISION Filed Nov. 14. 1966 2 Sheets-Sheet 2 Fig.4 8

Jnvenior: Hans-Dieter Schneider y g fink Allorney TRANSISTOR AMPLIFIERFOR CAPACITOR- COUPLED VERTICAL DEFLECTION COILS IN TELEVISIONHans-Dieter Schneider, Gross-Gerau, Germany, assignor to Fernseh GmbH,Darmstadt, Germany Continuation-impart of application Ser. No. 278,606,May 7, 1963. This application Nov. 14, 1966, Ser. No. 593,767

5 Claims. (Cl. 315-27) ABSTRACT OF THE DISCLOSURE A transistorizedcommon collector circuit for vertical deflection in televisionapparatus. The inherent stability features of the circuit are utilizedthrough a common emitter driving stage and a common collector outputstage. The common collector output stage energizes the deflection coilsof a cathode ray tube. A coupling capacitor is connected between theoutput stage and the deflection coil. A power supply is connected acrossthe emittercollector paths of both the driving stage and the outputstage. A voltage divider included in the power supply circuit appliesvoltages to the driving stage as well as to the output stage so that thetransistor of the common collector output stage is maintained in itsconducting state during the entire period of deflection of thedeflection coils, including the flyback interval.

The present invention relates to a transistor amplifier forcapacitor-coupled vertical deflection coils in television apparatus,utilizing substantially linear sawtooth signals. This application is acontinuation-in-part of my copending application Ser. No. 278,606, filedMay 7, 1963, now abandoned.

It is common practice to apply a transistorized common-emitter circuitfor the deflection stage in vertical deflection apparatus. Thisarrangement, however, has the disadvantage that its amplification variesconsiderably with temperature, the selected operating or quiescentpoint, and the voltage level of the power supply. These variationsaifect very adversely the stability of the deflection amplitude.

For the purpose of overcoming these disadvantages, one may apply acommon-collector circuit since its amplification is substantially unity.Assuming, hence, that one connects such a common-collector circuit to avertical deflection coil by way of a coupling capacitor, the latter isrequired to isolate the direct-current component in the circuit. Thislast or output stage may then be operated so that the transistor is madefurther conductive, during the retrace interval, as a result of theinductive energy of the coil. The latter, in form of a voltage peak,aflects the emitter in a manner such that the retrace or reset time isincreased to an extent that the requirements for proper operation of thetelevision apparatus cannot be met.

The preceding disadvantage results from the low output impedance of thecircuit as well as the further low impedance encountered by the feedback. This is especially reflected in the undesirable L/R ratio of thedeflection circuit comprising the deflection coil with its inductivity Land all ohmic resistances r and the generator impedance. The outputstage may, however, be operated so that the return energy affects thetransistor in a manner which cuts the latter off as a result of thedisplacement of its quiescent point through the null of thecharacteristic curve. The internal impedance of the transistor isthereby considerably increased, and the retrace cannot aperiodicallydecay during the retrace or reset time. As a result, severenonlinearities appear at the beginning of the forward trace due to thecurvature of the characteristic in States Patent 0 the vicinity of theinitial operating point of the transistor. Aside from this, it isnecessary to select a larger coupling capacitor due to the low outputimpedance of the common collector circuit. A smaller capacitor may beapplied with a common emitter circuit. Large coupling capacitors implyundesirably large dimensions of these components.

Accordingly, it is an object of the present invention to provide atransistorized common-collector circuit for vertical deflection intelevision apparatus, which is free from the aforementioned inherentdisadvantages.

Another object of the present invention is to provide a common collectorcircuit for vertical deflection in television apparatus, of thecharacter described, wherein the inherent stability features of thecircuit are utilized to realize the desired results.

A further object of the present invention is to provide a circuit, asdescribed, which is reliable in operation and may be maintainedeconomically.

A still further object of the present invention is to provide a circuit,as set forth, which may be readily manufactured and assembled.

With the preceding objects in view, the present invention comprises (a)A common-emitter driving stage including transistor means;

(b) A common-collector output stage including transistor means;

(c) Conductor means conductively connecting the collector of saidtransistor means of said driving stage to the base of the transistormeans of said output stage;

((1) Cathode-ray tube deflection coil means;

(e) Conductor means connecting said common-collector output stage tosaid cathode-ray tube deflection coil means;

(f) Coupling capacitor means arranged in said latter conductor means;

(g) A power supply connected to said common-collector output stage;

(h) First resistor means arranged in the connection between said powersupply and said common-collector output stage means; and

(i) Second resistor means connected between the collector of saidtransistor means of said common-emitter driving stage and the collectorof said transistor means of said common-collector output stage.

The output transistor of the circuit, in accordance with the presentinvention, is driven so that the voltage peaks, during retrace or reset,functions to cut ofi the circuit. Complete cut-off of the transistor,however, is inhibited through specific circuit elements. As a result,the disadvantage of a degenerating saw-tooth current, in flowing throughnonlinear parts of the characteristics, is avoided. At the same time,the coupling capacitor may be made smaller as nonlinearities during theforward trace resulting from an integrating effect of the capacitorappear at the base of the common collector stage and become more or lesscompensated. Therefore the electrolytic capacitors with theirundesirable thermal properties, may be dispensed with. A furtherimprovement provided by the present invention resides in the conditionthat the compensating action for the nonlinearities is performed in anoptimum manner. The invention also provides for considerable FIG. 1 is asimplified arrangement of the amplifier circuit, in accordance with thepresent invention;

FIG. 2 is an electrical circuit diagram showing an improvement over thearrangement of FIG. 1 with the inclusion of direct-current componentsassociated with the output signals;

FIG. 3 is an electric circuit diagram for deriving, furthermore, acontrol voltage; and

FIG. 4a including FIGS. 4b, and 4c is a graphical plot of curves showingthe operational conditions of the amplifier arrangement, in accordancewith the present invention.

Referring to the drawing, and in particular to FIG. 1, the latterrepresents a simple amplifier arrangement applicable to verticaldeflection currents in television apparatus. The transistor T isassociated with the last stage of the amplifier and is connected to forma common collector circuit. The load of this last stage of theamplifier, is composed of the deflection coils L in parallel with theresistors r. The load L is connected to the emitter of the transistor Tby way of the coupling capacitor C. The resistor R determines theoperating point and the quiescent current of the transistor T Theresistor R is substantially small compared to the load L, r.

In the collector circuit of the transistor T is the resistor R for thecoupling voltage. The resistor R is connected to the collector of thepreamplifying transistor T which is arranged in a common-emittercircuit. The voltage drop across the transistor T and the emitterresistor R determines further the operating point of the transistor TFor the purpose of clarifying the operation of the invention, and theselection of the magnitudes of the resistors R and R FIG. 4 may bereferred to. The latter is a graphical plot, as a function of time, of(A) the collector current I without feedback and J with feedback, (B) ofthe emitter potential U and the base potential U again without feedback,and (C) of the emitter potential U and the base potential U withfeedback. In accordance with the invention the magnitudes of theresistors R and R are selected, so that the instantaneous potential ofthe base of the transistor T U is higher than the emitter potentialthereof, during the entire saw-tooth period including the resettingtime, and the transistor T is in the conducting state. It is seen fromFIG. 4A and B that without the feedback coupling, the emitter potentialU moves in a direction which would cut off the transistor, as a resultof the ebbing of the energy stored in the deflection coils R during theretrace period if it were not for the presence of the resistors R and RThe consequence thereof would be, that the energy stored during theforward trace cannot decay completely during the reset period andaffects adversely the linearity at the beginning of the forward trace orsweep period, as shown in curve J M (FIG. 4A) at the part marked by thearrow.

Through selection of a relatively large coupling ratio as determinedmainly by the ratio R :R and the impedance of the driver stage, as forexample 1:10 the base potential exceeds, at all times, the emitterpotential of transistor T during the reset interval. In this manner, thetransistor T remains conducting and the reset energy may continuouslydecay during the time interval t As a result, the base potential assumesthe function shown by the curve U' The collector current I varies,accordingly, in the manner shown by the corresponding curve in FIG. 4A.

The coupling arrangement of resistors R and R also leads tolinearization of the emitter current during the forward trace interval tThus, the voltage level derived from the coupling arrangement, affectsthe base of the transistor T so that it compensates for the nonlinearityof the emitter potential resulting from the capacitor coupling. One can,thereby, determine the required negative feed back voltage of thecoupling arrangement through the consideration that the alternatingemitter voltage, amplified by transistor T is in phase with the voltageacross the collector resistor R The alternating emitter voltage isdetermined from the voltage divider comprising the resistor R theinternal resistance of the transistor T and the resistor R Since theinternal resistance of the transistor T is generally quite large, themagnitude of the feedback voltage is substantially dependent on theresistor R and the amplification factor of the transistor T Thesimplified embodiment of FIG. 1 has the particular disadvantage thatlosses are incurred by the alternating current signal as a result of theresistor R This disadvantage is overcome with the embodiment of FIG. 2.The circuitry of this embodiment includes an amplifier for the verticaldeflection of the electron beam for television tubes. For purposes ofillustrating the application of this circuit, the component valuesappear adjacent to the respective circuit elements in the diagram ofFIG. 2. The diagram includes, furthermore, the oscillographic voltagesof the base of the driving stage T collector of transistor T the base oftransistor T the base of transistor T as Well as the load L, r.

In transforming the circuitry of FIG. 1, the resistor R in FIG. 1 isreplaced by an additional transistor T in FIG, 2. If, now, a constantD-C level is applied to the base of this transistor T the latterfunctions as a filter choke and raises, thereby, the output of the laststage. This is due to the condition that the A-C current flows almostonly through the load L, r.

If, as shown in FIG. 2, an additional resistor R is connected in theemitter lead of driver transistor T and the emitter of this transistoris connected directly to the base of auxiliary transistor T then asignal voltage of the opposite polarity to that applied to the base ofoutput transistor T will be applied to the base of auxiliary transistorT The circuit then possesses the character of a complementary symmetryamplifier operating in class A, especially when, in contradistinction tothe arrangement shown in FIG. 2, transistor T is of the conductivitytype opposite to that of transistor T and T that is, of the n-p-n type.In such a circuit arrangement it is known to construct the driver stagein such a manner that the mutually antiphased modulating voltages whichit provides are of the same amplitude. This is attained by making theload resistors R and R of the driver stage equally large. According tothe invention, however, these resistors are of different values, R beingin fact of higher value than R so that with the negative feedback pathopen:

where:

h short-circuit current gain h =open-circuit voltage transfer h=short-circuit input resistance =amplification factor for an inputsignal at the base of T the collector of T serving as the outputelectrode.

6=amplification factor of transistor T in the commonemitterconfiguration, i.e. with the collector as output electrode and R as loadresistance.

If R is made larger than or equal to 500 ohms, then for the usual typesof transistor this may be written more simply:

In those cases where transistor T is of the p-n-p type, as illustratedin FIG. 2, this transistor performs essentially the same function asresistor R in FIG. 1. Modulation of T then produces only a smallincrease in gain, even when T and T are symmetrically modulated, sincethe output impedance of T is effectively the load impedance of T andthis has a value small compared with that of R The output voltageappearing at point A in the circuit is thus determined substantially bythe modulating voltage applied to the base of transistor T In this case,therefore, it is not necessary that T shall receive the same modulationvoltage as T Resistor R may therefore be chosen with regard to the factthat the voltage drop across it serves to set the working points oftransistors T and T owing to the fact that the emitter of transistor Tis connected directly to the base of transistor T The bias voltage forthe base of transistor T may be produced in a simple manner byconnecting the base of transistor T directly with the collector oftransistor T The gain V' of the circuit is then described withsufiicient accuracy by the equation:

where the symbols are as previously defined.

The efliciency of the output stage may be considerably improved by theuse of this circuit arrangement. Although a push-pull circuit is notutilized this being realizable only by the use of a transistor of thecomplementary conductivity type, it becomes possible to compensate inthis manner for the possible disadvange of increased load or workingvoltage being required by the resistor in the collector lead of theoutput stage transistor.

In known applications of amplifiers of this general type it has beenproposed to provide means for producing gain control of the amplifieritself, or alternatively of the signal source from which it is fed, sothat a constant signal current amplitude is produced in the loadimpedance. This may be achieved by rectifying the signal voltageappearing across an auxiliary resistor connected in series with the loadimpedance and employing the rectified voltage to control the gain. Intransistor amplifiers according to the invention it is advantageous toderive the gain-control voltage across the auxiliary resistor in thecollector lead of the output transistor, instead of from a resistor inseries with the load impedance. Such an arrangement is shown in FIG. 3,the amplifier portion of which is identical with that of FIG. 2. Here,however, the signal potentials appearing at the collector of transistorT are applied by way of a capacitor C to the junction of two opposeddiodes D D which thus develop across a capacitor C a control voltagedependent upon the magnitude of the output current. This control voltageis made use of in known manner to control the amplitude of the signalapplied to the amplifier in such a manner as to main tain the amplitudeof the output current substantially constant.

What is claimed as new and desired to be secured by Letters Patent is:

1. A transistor amplifier for television apparatus comprising, incombination, a common-emitter driving stage includin-g transistor means;a common-collector output stage including transistor means; conductormeans conductively connecting the collector of said transistor means ofsaid driving stage to the base of the transistor means of said outputstage; cathode-ray tube deflection coil means; coupling capacitor meansconnected between said common-collector output stage and saidcathode-ray tube deflection coil means; a power supply connected to saidcommon-collector output stage; first resistor means connected betweensaid power supply and said commoncollector output stage means; secondresistor means connected between the collector of said transistor meansof said common-emitter driving stage and the collector of saidtransistor means of said common-collector output stage; biasingtransistor means for biasing the transistor means of saidcommon-collector output stage; and a resistor connected between theemitter of said biasing transistor means and said power supply, wherebysaid transistor means of said common-collector output stage ismaintained in its conducting state during the period of deflection ofsaid deflection coils.

2. A transistor amplifier for television apparatus comprising, incombination, a common-emitter driving stage including transistor means;a common-collector output stage including transistor means; conductormeans conductively connecting the collector of said transistor means ofsaid driving stage to the base of the transistor means of said outputstage; cathode-ray tube deflection coil means; conductor meansconnecting said common-collector output stage to said cathode-ray tubedeflection coil means; coupling capacitor means arranged in said latterconductor means; a power supply connected across the emitter-collectorpaths of said common-collector output stage and said common-emitterdriving stage; first resistor means connected between said power supplyand the collector of said transistor means of said common-collectoroutput stage means; second resistor means connected between thecollector of said transistor means and said common-emitter driving stageand the collector of said transistor means of said common-collectoroutput stage; biasing transistor means the collector of which isconnected to the emitter of the transistor means of saidcommon-collector output stage for biasing the same, the base of saidbiasing transistor means being connected to the emitter of saidtransistor means of said driving stage; and a resistor connected betweenthe emitter of said biasing transistor means and said power supply,whereby said transistor means of said common-collector output stage ismaintained in its conducting state during the period of deflection ofsaid deflection coils.

3. A transistor amplifier as defined in claim 2 including a thirdresistor means in the emitter of said transistor means of said commonemitter driving stage.

4. A transistor amplifier as defined in claim 3 wherein the base of saidbiasing transistor is connected to said third resistor and to theemitter of the transistor means of said common emitter driving stage.

5. A transistor amplifier as defined in claim 4 wherein said thirdresistor means is substantially smaller than said second resistor means.

References Cited UNITED STATES PATENTS 2,750,456 6/1956 Waldhauer 330-28X 3,079,566 2/1963 Ebbinge 330-20 3,098,199 7/1963 Carney et al. 330-293,125,693 3/1964 De Clue 330-18 X 3,167,721 1/1965 Broadhead 330-28 XFOREIGN PATENTS 153,370 4/ 1952 Australia.

OTHER REFERENCES Single Ended Amplifiers for Class B operation by Lin etal. Electronics Magazine, May 29, 1959, pp. 86-87.

Cathode Ray Tube Displays (book) by Soller, Starr, Valley. Received inUs. Patent Office, Sept. 1, 1948 pp. 359460.

RODNEY D. BENNETT, Primary Examiner. JOHN W. CALDWELL, Examiner.

R. K. ECKERT, JR., J. D. BAXTER, Assistant Examiners.

